Communication apparatus and communication control method

ABSTRACT

The communication apparatus installed in an aircraft can communicate wirelessly with another communication apparatus. The communication apparatus comprises a controller (110) and a transmitter (106). The controller (110) acquires altitude information of the aircraft and determines transmission power according to the altitude information. The transmitter (106) transmits transmission data to another communication apparatus using the determined transmission power.

TECHNICAL FIELD

The present disclosure relates to a wireless communication apparatus anda wireless communication control method to be used in aircraft.

BACKGROUND

Demand for making a wireless communication environment in aircraft isincreasing. For this purpose, the Wireless Avionics Intra-Communication(WAIC) system has been standardized as a wireless communication systemin aircraft. As the wireless frequency band used by communicationapparatuses in the WAIC system, the 4.2 GHz to 4.4 GHz band has beenallotted by the ITU.

SUMMARY OF INVENTION Problem to be Solved by Invention

A radio altimeter that measures the altitude of aircraft using radiowaves of the 4.2 GHz to 4.4 GHz band is installed in aircraft.Therefore, the radio waves from the communication apparatus (wirelessdevice) of the WAIC system possibly interfere with those from the radioaltimeter. This could cause malfunction of the radio altimeter orcommunication jamming between the communication apparatuses in aircraft.

Several communication methods for avoiding interference with a radioaltimeter have been proposed (see Patent Document 1, Patent Document 2,and Patent Document 3). However, because the environment inside andoutside aircraft change in various ways, it is required to enable stablewireless communication even if such changes occur.

Means for Solving the Problems

An object of the present disclosure is to provide a communicationapparatus and a communication control method that are effective forpreventing the influence of radio wave interference between a radioaltimeter and a communication apparatus in aircraft.

The communication apparatus in the present disclosure is a communicationapparatus configured to be installed in an aircraft and communicatewirelessly with one other communication apparatus. The communicationapparatus comprises a controller and a transmitter. The controller isconfigured to acquire altitude information of the aircraft and determinetransmission power according to the altitude information. Thetransmitter is configured to transmit transmission data to the one othercommunication apparatus using the determined transmission power.

Effect of Invention

The communication apparatus and the communication control methodaccording to the present disclosure are effective for preventing theinfluence of radio wave interference between the radio altimeter and thecommunication apparatus in aircraft.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 schematically shows a radio altimeter installed in an aircraft.

FIG. 2 shows a signal waveform of a radio altimeter.

FIG. 3 shows an internal configuration of an FMCW type radio altimeter.

FIG. 4 shows a relationship between a beat signal of a radio altimeterand a bandwidth of a reception LPF.

FIG. 5 shows a configuration of a communication apparatus according toEmbodiment 1;

FIG. 6 shows an example of control information for transmission power.

FIG. 7 shows an example of control information for transmission power.

FIG. 8 shows an example of control information for transmission power.

FIG. 9 shows a configuration of a communication apparatus according toEmbodiment 2;

FIG. 10 shows a relationship between the transmission frequency of aradio altimeter and the bandwidth of a communication apparatus.

FIG. 11 shows a relationship between the transmission frequency of aradio altimeter and the bandwidth of a communication apparatus.

FIG. 12 shows a received signal of a communication apparatus withrespect to the time axis.

FIG. 13 shows a transmission frame.

FIG. 14 shows a state of transmission frames transmitted from acommunication apparatus.

FIG. 15 shows a relationship between the transmission frequency of aradio altimeter and the bandwidth of a communication apparatus.

FIG. 16 shows a relationship between the transmission frequency of aradio altimeter and the bandwidth of a communication apparatus.

FIG. 17 shows a configuration of a communication apparatus according toEmbodiment 3.

FIG. 18 shows a relationship between the transmission frequency of aradio altimeter and the bandwidth of a communication apparatus.

FIG. 19 shows a transmission frame transmitted from a communicationapparatus.

FIG. 20 shows a relationship between the transmission frequency of aradio altimeter and the bandwidth of a communication apparatus.

FIG. 21 shows a relationship between the transmission frequency of aradio altimeter and the bandwidth of a communication apparatus.

FIG. 22 shows an example of a transmission frame.

FIG. 23 shows a relationship between the transmission frequency of aradio altimeter and the bandwidth of a communication apparatus.

FIG. 24 shows a relationship between the transmission frequency of aradio altimeter and the bandwidth of a communication apparatus.

FIG. 25 shows a relationship between the transmission frequency of aradio altimeter and the bandwidth of a communication apparatus.

FIG. 26 shows a configuration of a communication apparatus according toEmbodiment 4.

FIG. 27 shows amplitudes of received signals of a radio altimeter whenweight is changed.

FIG. 28 shows a configuration of a communication apparatus according toEmbodiment 5.

FIG. 29 shows an example of a waveform of a transmission signal from aradio altimeter.

FIG. 30 shows an example of a waveform of a transmission signal from aradio altimeter.

FIG. 31 shows an example of a waveform of a transmission signal from aradio altimeter.

FIG. 32 shows an example of a waveform of a transmission signal of aradio altimeter.

FIG. 33 shows an example of a waveform of transmission signals of aradio altimeter.

FIG. 34 shows positions of a plurality of communication apparatuses inaircraft.

FIG. 35 shows a configuration of a control apparatus according toEmbodiment 6.

FIG. 36 shows a configuration of a communication apparatus according toEmbodiment 6.

FIG. 37 shows antenna directivities of a plurality of communicationapparatuses according to Embodiment 7.

FIG. 38 shows a plurality of communication apparatuses and a radioaltimeter installed in an aircraft according to Embodiment 8.

FIG. 39 shows a configuration of a communication apparatus according toEmbodiment 8.

FIG. 40 shows a configuration of a communication apparatus according toEmbodiment 9.

FIG. 41 shows a state of a transmission signal transmitted by acommunication apparatus according to Embodiment 9.

FIG. 42 shows a plurality of communication apparatuses and a radioaltimeter installed in an aircraft according to Embodiment 10.

FIG. 43 shows a configuration of a control apparatus according toEmbodiment 10.

FIG. 44 shows positions of a plurality of aircraft in Embodiment 11.

FIG. 45 shows a configuration of a communication apparatus according toEmbodiment 11.

FIG. 46 shows a positional relationship between a plurality ofcommunication apparatuses installed in an aircraft and a radio altimeterinstalled in another aircraft, according to Embodiment 12.

FIG. 47 shows a plurality of communication apparatuses and a radioaltimeter installed in an aircraft according to Embodiment 13.

FIG. 48 shows a spectrum of an interference signal of a radio altimeterand a received signal of a communication apparatus.

FIG. 49 shows a spectrum of an interference signal of a radio altimeterand a received signal of a communication apparatus.

FIG. 50 shows a configuration of a receiver of a communication apparatusaccording to Embodiment 13.

FIG. 51 shows a spectrum of an interference signal of a radio altimeterand a received signal of a communication apparatus according toEmbodiment 13.

FIG. 52 shows a spectrum of an interference signal of a radio altimeterand a received signal of a communication apparatus according toEmbodiment 13.

FIG. 53 shows a spectrum of an interference signal of a radio altimeterand a received signal of a communication apparatus according toEmbodiment 13.

FIG. 54 shows a spectrum of an interference signal of a radio altimeterand a received signal of a communication apparatus according toEmbodiment 13.

DETAILED DESCRIPTION

Hereinafter, the Embodiments will be described in detail with referenceto the drawings as appropriate. Any explanations deemed unnecessary maybe omitted. For example, detailed descriptions of well-known aspects orduplicate descriptions of substantially identical components may beomitted from this disclosure.

It is to be noted that the attached drawings and the followingdescription are provided to enable those skilled in the art to fullyunderstand the present disclosure, and they are not intended to limitthe claimed subject matter.

<Radio Altimeter>

FIG. 1 schematically shows a radio altimeter 2 that is mounted at thebottom 10 b of an aircraft 1. The radio altimeter 2 comprises atransmitter 3 and a receiver 4. The transmitter 3 transmits transmissionwaves TW. The transmission waves TW are radiated downward (towards theground surface G) from the bottom 10 b of the aircraft 1. Thetransmission waves TW are reflected by the ground surface G and thenreceived by the receiver 4 as reception waves RW that are reflectedwaves. At this time, the reception waves RW are received by the receiver4 with a time delay with respect to when the transmission waves TW weretransmitted by the transmitter 3. The time delay equals(2×altitude)/light speed. Therefore, it is possible to find the altitudeof the aircraft 1 from this time delay.

FIG. 2 shows a wave form of signals from the radio altimeter 2. Radioaltimeters which utilize frequency-modulated continuous waves (FMCW) arewidely used as radio altimeters in civilian aircraft. The FMCW typeradio altimeter transmits transmission waves by modulating the frequencyof carrier waves. As shown in FIG. 2, the frequency of carrier waves inthe transmission waves TW from the transmitter 3 is continuously sweptin a given frequency width to form a sweep waveform. The sweep waveformis a triangle wave and, in many cases, the sweep frequency is for 50 to300 Hz. The transmitter 3 performs the modulation so as to increase thefrequency of carrier waves as the level of the sweep waveform getshigher and decrease the frequency of carrier waves as the level of thesweep waveform gets lower.

As stated above, the radio altimeter 2 operates in the 4.2-4.4 GHz band.Of the 200 MHz frequency bandwidth that can be used by the radioaltimeter 2, the 100 to 150 MHz which is a mid band is often used. Thetransmission power ranges from 10 mW (+10 dBm) to 500 mW (+27 dBm).

Since the reception waves RW received by the receiver 4 are delayedcompared with the transmission waves TW, the frequency of the receptionwaves RW differ from the frequency of the transmission waves TW. If thechange (sweep) rate of the frequency of the transmission waves TW isconstant, the delay time, i.e. altitude, is directly proportional to thedifference in the measured frequencies of the transmission waves TW andthe reception waves RW.

FIG. 3 shows a general internal configuration of a FMCW-type radioaltimeter. The receiver 4 including a reception antenna inputs receptionwaves into a frequency mixer 22. The frequency mixer 22 outputs thedifference in the frequencies of the transmission waves and thereception waves. The transmitter 3 including a transmission antennainputs part of the transmission waves into the homodyne-type frequencymixer 22. The output is inputted into the reception low-pass filer(LPF). The reception LPF 24 detects a beat signal, which is thefrequency difference between the transmitter 3 and the receiver 4 fromthe output of the reception mixer 22.

The frequency counter 26 detects the frequency of the beat signal (beatfrequency). In many cases, the beat frequency is 1 MHz or less. Theradio altimeter 2 estimates an altitude from the beat frequency, andoutputs the altitude to an alarm unit 27 and an altitude indicator 28.As the beat frequency is higher, the time delay Δt in FIG. 2 is larger,and whereas the beat frequency is lower, the time delay Δt in FIG. 2 issmaller.

The radio altimeter 2 is provided with a sweep generator 29 and avoltage-controlled oscillator 30 for generating transmission waves. Thesweep generator 29 generates a triangle sweep waveform. Thevoltage-controlled oscillator 30 inputs the generated sweep waveformsignals to generate radio signals of which frequency varies according tothe voltage values corresponding to the sweep waveform. The generatedradio waves are transmitted by the transmitter 3 after passing thebuffer amplifier 31.

FIG. 4 shows a relationship between the beat signal and the bandwidth ofthe reception LPF 24. The frequency mixer 22 multiplies the transmissionfrequency ft and reception frequency fr of the radio altimeter 2, andfrom the ft+fr component and ft−fr component obtained as the result,extracts only the differential component (ft−fr) corresponding to thebeat signal by the LPF 24. The bandwidth Blpf of the reception LPF 24 isdesigned to be greater than the beat frequency, and to be smaller thanthe sum component (ft+fr).

As stated above, a typical radio altimeter continuously uses the 200 MHzbandwidth, centered on 100 to 150 MHz, in the 4.2 to 4.4 GHz bandassigned in the WAIC system. For that reason, interference occurs due toa communication apparatus of the WAIC system using the same frequencyband as the radio altimeter. In particular, when an interferencecomponent is included in the received signal of the radio altimeter, anerror may result in the cruising altitude of an aircraft which couldinterfere with safe flight. Therefore, such interference must beavoided.

The present disclosure relates to a communication apparatus adopting atransmission method that does not cause interference with a radioaltimeter and therefore, the communication apparatus can use thefrequency band used by the radio altimeter. For example, thecommunication apparatus transmits a transmission signal so as to preventthe transmission signal from being included in the bandwidth Blpf of thereception LPF 24 in the radio altimeter as shown in FIG. 4, therebyavoiding interference with the radio altimeter. For example, asdescribed later, a frequency spectrum of the transmission signal iscontrolled so that the absolute value of a difference between thefrequency used for the transmission signal of the communicationapparatus and the frequency used for the transmission signal of theradio altimeter is greater than a cutoff frequency of the LPF applied tothe received signal of the radio altimeter. When the signal from thecommunication apparatus is out of the bandwidth Blpf of the receptionLPF 24, the signal is cut off by the reception LPF 24 of the radioaltimeter, thereby causing no interference with the radio altimeter. Inother words, the communication apparatus transmits and receives signalsusing a frequency range out of the bandwidth of the reception LPF 24 inthe radio altimeter, according to the timing of a frequency sweep of theradio altimeter.

Embodiment 1

According to this embodiment, the communication apparatus used in anaircraft changes its transmission power for transmitting a radio signalin accordance with an altitude of the aircraft.

FIG. 5 shows the configuration of a communication apparatus 100according to Embodiment 1. The communication apparatus 100 comprises anantenna 111, a receiver 102, a decoder 103, a communication controller104, an encoder 105, a transmitter 106, an altitude informationacquisition unit 107, and a transmission power controller 108.

In the communication apparatus 100, a signal received by the antenna 111is sent to the receiver 102. The receiver 102 performs receptionprocessing and transmits the received signal, which has beendigitalized, to the decoder 103.

The communication apparatus 100 includes a processor 110 includingelectronic circuitry such as a CPU. The processor 110 executes controland calculation for the communication apparatus according to apredetermined algorithm, thereby preforming the functions of the decoder103, the communication controller 104, the encoder 105, the altitudeinformation acquisition unit 107, and the transmission power controller108.

The decoder 103 decodes the received signal to extract reception data.The communication controller 104 reads a destination address included inthe reception data, and when the reception data is addressed to thecommunication apparatus itself, performs processing of the receptiondata.

The altitude information acquisition unit 107 acquires altitudeinformation of the aircraft 1, and transmits the acquired altitudeinformation to the communication controller 104. The method foracquiring altitude information of the aircraft 1 by the altitudeinformation acquisition unit 107 may include acquiring the presentaltitude by connecting to the radio altimeter 2 or another instrument,receiving a notification from another communication apparatus that holdsthe altitude information, acquiring by a crew member of the aircraftinputting the altitude information, or such other method.

When the communication apparatus 100 transmits a signal to anothercommunication apparatus, the communication controller 104 determinesgeneration of data to be transmitted and transmission parameters. Thetransmission parameters include an encoding scheme, an encoding rate, amodulation scheme, a frequency band, precoding information, a channel tobe used, transmission power, or such other parameter. Based on thealtitude information acquired by the altitude information acquisitionunit 107, the communication controller 104 determines the transmissionpower of the communication apparatus 100, and transmits the transmissionpower figure to the transmission power controller 108.

As one example, the communication controller 104 will determine thetransmission power in accordance with the conditions shown in FIG. 6.When the altitude information indicates the altitude of the aircraft 1is 4000 feet or greater, the communication controller 104 uses 10 dBm asthe transmission power. In contrast, when the altitude of the aircraft 1is less than 4000 feet, the communication controller 104 uses 1 dBm asthe transmission power.

Accordingly, when the altitude of the aircraft 1 is low and the radioaltimeter 2 is operating, the communication apparatus 100 can reduce theeffect of interference with the radio altimeter 2 by reducing thetransmission power to a low level. In contrast, when the altitude of theaircraft 1 is high and the radio altimeter 2 is not operating, there isno need to consider the effect of interference with the radio altimeter2, and therefore, the communication apparatus 100 performs communicationusing a high transmission power. The switching of the transmission powerusing 4000 feet as the boundary in FIG. 6 is an example in which thealtitude at which use of the radio altimeter 2 is to be stopped is 4000feet. The boundary value for the transmission power switching may be avalue in accordance with the type of a radio altimeter being used or anactual operation. The value of transmission power is also exemplary andmay be another value.

The communication controller 104 transmits transmission data to theencoder 105. The encoder 105 performs an encoding process on thetransmission data in accordance with the parameters defined by thecommunication controller 104 and creates encoded data. The transmitter106 modulates the encoded data and transmits the data from the antenna111. At this time, the transmission power controller 108 performscontrol such that the transmission power of the transmission signal tobe transmitted from the transmitter 106 is equal to the transmissionpower value determined by the communication controller 104.

The present embodiment has described the communication controller 104using two transmission power values in accordance with the altitudeinformation, but the number of the power is not necessarily limitedthereto. Three or more transmission power values may be used. Forexample, as shown in FIG. 7, the communication controller 104 may use adetermination method in which the transmission power of thecommunication apparatus 100 increases as the altitude indicated by thealtitude information decreases while the radio altimeter 2 is operating.

Since the receiver 4 of the radio altimeter 2 shown in FIG. 3 receivesradio waves transmitted by the transmitter 3 and reflected by the groundsurface, the reception power of the radio altimeter 2 is generallyhigher at lower altitudes. For that reason, when a SIR(signal-to-interference power ratio) that does not affect the operationof the radio altimeter 2 is made constant regardless of the altitude,higher interference power is acceptable at lower altitudes.

Note that in the present embodiment, while the altitude informationacquisition unit 107 was described as acquiring altitude information ofthe aircraft 1, the altitude information may be a value expressing theactual altitude, or may be a value obtained by encoding the altitudevalue. For example, even in the case of the altitude information beingexpressed by binary symbols, it is possible to achieve the effect of thepresent invention.

In the present embodiment, the communication controller 104 wasdescribed as performing control that determines the transmission powerin accordance with the altitude information, but the communicationcontroller 104 may also perform control to determine a modulation codingscheme (MCS) in accordance with the transmission power. In this case,when the altitude of the aircraft is high so that interference with theradio altimeter 2 is not a problem, the communication controller 104determines a high transmission power and selects an MCS with manymodulation levels and a high encoding rate. In contrast, when thealtitude of the aircraft 1 is low and interference with the radioaltimeter could occur, the communication controller 104 determines a lowtransmission power and selects an MCS with few modulation levels and alower encoding rate. As a result, the communication apparatus 100, evenwith low transmission power, can lower the MCS so as to achievecommunication with a low bit error probability.

In addition, as a method of controlling the transmission power, thecommunication controller 104 may adopt a process that spreads thetransmission signal and lowers the transmission power per unitfrequency. In this case, the transmitter 106 may generate a spreadspectrum signal by performing a spreading process when performing themodulation processing of the encoded data, and transmit the signal fromthe antenna 111. As a result, it is possible to lower the interferencepower at the frequency being used by the radio altimeter 2.

As described above, the communication apparatus 100 according to thepresent disclosure can operate such that the SI ratio, which is a ratiobetween reception power of the radio altimeter 2 and interference powerfrom the communication apparatus 100, can be a sufficiently high valuethat does not affect the operation of the radio altimeter 2. Therefore,the communication by the communication apparatus 100 can suppressinterference with the radio altimeter 2 and can be used even in thefrequency band used by the radio altimeter 2.

Embodiment 2

When the radio altimeter 2 is transmitting a signal using a frequency incertain frequency channels, the communication apparatus 200 according tothe present embodiment executes communication control so that thecommunication does not use a frequency in the frequency channels.

FIG. 9 shows the configuration of a communication apparatus 200according to this embodiment. The communication apparatus 200 comprisesan antenna 211, a receiver 202, a decoder 203, a communicationcontroller 204, an encoder 205, and a transmitter 206.

The communication apparatus 200 transmits a signal received by theantenna 211 to the receiver 202. The receiver 202 performs receptionprocessing and transmits the received signal, which has been digitized,to the decoder 203.

The communication apparatus 200 includes a processor 110 includingelectronic circuitry such as a CPU. The processor 210 executes thefunctions of the decoder 203, the communication controller 204, and theencoder 205 by performing control and calculation according to apredetermined algorithm.

The decoder 203 decodes the received signal to extract reception data.The communication controller 204 reads a destination address included inthe reception data, and when the reception data is addressed to thecommunication apparatus itself, performs processing of the receptiondata.

During a transmission operation, the communication controller 204controls a transmission timing so as to transmit transmission data at atiming when the radio altimeter 2 is not using the frequency channelcurrently used by the communication apparatus 200. When the transmissionis possible, the communication controller 204 transmits the transmissiondata to the encoder 205. The encoder 205 encodes the transmission data.The transmitter 206 modulates the encoded transmission data to generatea transmission signal, and transmits the transmission signal to theantenna 211.

Next, a method in which the communication apparatus 200 estimates thetiming at which the radio altimeter 2 uses the corresponding frequencychannel will be discussed.

As shown in FIG. 10, it is assumed that the communication apparatus 200uses the frequency channel CHa in the bandwidth Bwaic. The transmissionfrequency fra of the radio altimeter 2 has been repeatedly swept fromthe lower limit to the upper limit of the frequency bandwidth Bra of theradio altimeter 2. In FIG. 10, the transmission frequency fra of theradio altimeter 2 is outside the frequency channel CHa which is beingused by the communication apparatus 200.

The communication apparatus 200 performs carrier sense. When a signalfrom another communication apparatus is not received, a received signal(carrier) is not observed in the receiver 202 of the communicationapparatus 200.

Next, as shown in FIG. 11, when the transmission frequency fra of theradio altimeter 2 is in the frequency channel CHa of the communicationapparatus 200, the transmission signal of the radio altimeter 2 appearsin the receiver 202 of the communication apparatus 200.

FIG. 12 shows a state of the received signal of the communicationapparatus 200 with respect to time. In FIG. 12, the period from time t1to t2 is the time during which the frequency fra of the transmissionsignal of the radio altimeter 2 is in the frequency channel CHa. Thereceived signal is observed at the receiver 202 of the communicationapparatus 200. The same applies between time t3 and time t4 and betweentime t5 and time t6.

Here, the communication apparatus 200 can estimate the frequency sweepperiod of the radio altimeter 2 by observing the time interval at whichthe waveform appears in the reception waveform at the receiver 202.Based on this period, the communication controller 204 of thecommunication apparatus 200 estimates the timing when the transmissionsignal of the radio altimeter 2 is not using the frequency in thefrequency channel CHa, that is, the timing when no interference is givento the radio altimeter 2, and transmits the transmission data at thattiming.

The interference with the radio altimeter 2 occurs in the receiver 4(FIG. 3) of the radio altimeter 2. Therefore, the time in which nointerference with the radio altimeter 2 occurs can be assumed to followthe time difference Δt added to the time when the signal transmittedfrom the radio altimeter 2 does not appear at the receiver 202 of thecommunication apparatus 200, the time difference Δt being from when thesignal is transmitted from the transmitter 3 of the radio altimeter 2 towhen the signal reaches the receiver 4 after reflected by the groundsurface. The Δt varies depending on a navigation altitude of aircraft.Therefore, the communication controller 204 may use the time differenceΔt at the highest altitude when the radio altimeter 2 can be used, orthe time difference Δt at the highest altitude when measurement by theradio altimeter 2 is guaranteed. Accordingly, the interference with theradio altimeter 2 can be avoided without depending on the altitude.

Note that the communication apparatus 200 transmits transmission data inframes, which is an example of a unit length of transmission data, asshown in FIG. 13. The time for transmission of a transmission frame bythe communication apparatus 200 may be taken longer than a time from thecurrent time to the time t1 when the radio altimeter 2 uses Cha for itsnext transmission. If this is expected, the communication controller 204of the communication apparatus 200 may divide the transmission data toproduce two transmission frames.

The communication controller 204 sets the length of the transmissionframe A shown in FIG. 14 to a length that allows transmission to becompleted between the current time and the time t1. The communicationapparatus 200 transmits the transmission frame B after the radioaltimeter 2 starts not to use a frequency in the CHa for itstransmission signal. In this way, even when the size of the transmissiondata is large, the transmission data can be sent without causinginterference with the radio altimeter 2.

Although the case where the transmission frame is divided into two hasbeen described above, the present disclosure is not limited thereto. Theeffect of the present disclosure can be obtained even when thetransmission frame is divided into three or more, or even when thetransmission interval between the divided transmission frames iswidened.

In a case where the communication apparatus 200 divides the transmissionframe into two or more, if another communication apparatus that hasreceived the transmission frame A transmits an ACK frame, this couldcause interference with the radio altimeter 2. In such a case, thecommunication apparatus 200 may use the block ACK function, by which ACKfor a plurality of data is collectively returned, thereby preventinganother communication apparatus from transmitting an ACK frame after thetransmission of the transmission frame A.

Embodiment 3

The communication apparatus 300 according to this embodiment performscommunication using a frequency band other than the frequency band whichis being used by the radio altimeter 2.

Here, a communication apparatus that performs broadband transmission istaken into consideration. For example, in the case of the communicationapparatus 200 of Embodiment 2, when the bandwidth used by thecommunication apparatus is equal to or wider than the bandwidth used bythe radio altimeter 2, there is no time in which the communicationapparatus can transmit a signal because the receiver 202 keeps detectingthe transmission frequency fra of the radio altimeter. Further, as shownin FIG. 15 and FIG. 16, even when the bandwidth CHb used by thecommunication apparatus is narrower than the bandwidth Bra used by theradio altimeter 2, if the major parts thereof overlap, there arises aproblem that the time during which the communication apparatus cantransmit a signal is reduced. Accordingly, this embodiment describes acommunication apparatus that can operate even in such a state.

FIG. 17 shows a communication apparatus 300 of this embodiment. Thecommunication apparatus 300 has a similar configuration as thecommunication apparatus 200 of Embodiment 2 and includes an antenna 311,a receiver 302, a decoder 303, a communication controller 304, anencoder 305, and a transmitter 306.

The communication apparatus 300 includes a processor 310 includingelectronic circuitry such as a CPU. The processor 310 executes thefunctions of the decoder 303, the communication controller 304, and theencoder 305 by performing control and calculation according to apredetermined algorithm.

In particular, the communication apparatus 300 transmits a signal havinga spectrum S11 shown in FIG. 18 in order to avoid interference with theradio altimeter 2. As shown in FIG. 18, the spectrum S11 includes aspectrum notch having a bandwidth of Bnull including the frequency fraused by the radio altimeter 2. Here, the communication controller 304 inthe communication apparatus 300 sets the bandwidth Bnull of the spectrumnotch so as to satisfy the following criteria.

A beat frequency corresponding to the maximum measurable altitude Hmaxsupported by the radio altimeter 2 is referred to as fbmax, and thebandwidth of the reception LPF of the radio altimeter 2 is referred toas Bldf.

As shown in FIG. 19 to FIG. 21, the difference between the transmissionfrequency fra1 and the transmission frequency fra2 is referred to asfadiff, in which the fra1 is a transmission frequency of the radioaltimeter 2 at the transmission start time is of a transmission frametransmitted by the communication apparatus 300 as shown in FIG. 19, andthe fra2 is a transmission frequency of the radio altimeter 2 at thetransmission end time to of the transmission frame.

By setting the value of Bnull to be a larger than a value found by theformula below, the communication apparatus 300 can transmit atransmission frame without causing interference with the radio altimeter2.

fbmax+Blpf+fadiff  Formula 1:

Further, the communication controller 304 sets the lower limit and upperlimit frequencies of Bnull as below.

fra1−(fbmax+Blpf)  Formula 2:

fra2+(fbmax+Blpf)  Formula 3:

Note that although the communication controller 304 of this embodimentuses the maximum value fbmax as the beat frequency, the presentdisclosure is not limited to this. Alternatively, the beat frequencyfbnow corresponding to the current altitude of aircraft may be used. Bydoing so, the communication apparatus 300 can reduce the width of Bnull,and can increase the amount of data that can be transmitted in thetransmission frame.

The transmitter 306 in the communication apparatus 300 generates atransmission signal having a spectrum determined by the communicationcontroller 304. The method of generating a transmission signal having aspectrum with a notch may adopt setting subcarriers of a multicarriersignal such as OFDM, which correspond to the Bnull frequency, to zero,applying weight for precoding, or deforming the spectrum bysuperimposing another delayed transmission signal for a predeterminedtime.

In the above described embodiment, it has been described that thecommunication controller 304 nullifies the frequency including thetransmission frequency of the radio altimeter 2 when transmission of thetransmission frame ends. However, if the transmission frame is long andthe difference between the fadiff and the bandwidth Bwaic2 of thecommunication apparatus 300 gets smaller, it becomes necessary toincrease the Bnull, which will cause the bandwidth available fortransmission to be narrower. In such a case, the communicationcontroller 304 avoids interference with the radio altimeter 2 bychanging the position of the Bnull for each transmission symbolconstituting the transmission frame as shown in FIG. 22 to FIG. 25,thereby enabling a long transmission frame to be transmitted.

Embodiment 4

This embodiment describes a communication apparatus that includes anadaptive antenna array that can electrically control directivity, thecommunication apparatus being configured to perform communication withan antenna directivity pattern that minimizes signal power from theradio altimeter.

FIG. 26 shows a communication apparatus 400 in this embodiment. Thecommunication apparatus 400 comprises an antenna array 411, a receiver402, a communication controller 404, and a transmitter 406.

The communication apparatus 300 includes a processor 410 includingelectronic circuitry such as a CPU. The processor 410 executes thefunctions of the decoder 403, the communication controller 404, and theencoder 405 by performing control and calculation according to apredetermined algorithm.

The antenna array 411 is an antenna array including a plurality ofantenna elements. The receiver 402 synthesizes signals obtained bymultiplying signals received by the antenna elements of the antennaarray 411 with a weight (amplitude change, phase rotation). Here, amethod for determining the weight applied by the receiver 402 will bedescribed.

FIG. 27 shows amplitude of a received signal by the radio altimeter 2when the receiver 402 changes the weight. FIG. 27 shows an example ofamplitude of the received signal when the weight is changed between W1,W2, and W3. By changing the weight, the amplitude of the received signalchanges. If a weight pattern that generates the smallest amplitude ofthe received signal is used, interference with the radio altimeter 2 isminimized.

In addition, when the communication apparatus 400 switches betweentransmission and reception using time division duplex (TDD), if theweight pattern used for reception is also used for transmission,interference with the radio altimeter 2 can be reduced.

Thus, the communication apparatus 400 of this embodiment changes theweight pattern in the receiver 402 to a weight pattern that minimizesthe amplitude of the received signal from the radio altimeter 2, therebyreducing interference to the radio altimeter 2 and from the radioaltimeter 2.

Embodiment 5

This embodiment describes a communication apparatus that changesparameters for transmitting a radio signal depending on the altitude ofaircraft.

FIG. 28 shows the configuration of a communication apparatus 500. Thecommunication apparatus 500 comprises an antenna 511, a receiver 502, adecoder 503, a communication controller 504, an encoder 505, atransmitter 506, and an altitude information acquisition unit 507,similarly to the communication apparatus 100 of Embodiment 1. Likewisethe communication apparatus 100 of the Embodiment 1, the communicationapparatus 500 includes a processor 510 including electronic circuitrysuch as a CPU. The processor 510 executes the functions of the decoder503, the communication controller 504, the encoder 505, and the altitudeinformation acquisition unit 507 by performing control and calculationaccording to a predetermined algorithm.

When the communication apparatus 500 transmits a signal to anothercommunication apparatus, the communication controller 504 acquires thecurrent altitude information from the altitude information acquisitionunit 507. The communication controller 504 determines generation oftransmission data and transmission parameters based on the acquiredaltitude information. The transmission parameters include a codingscheme, a coding rate, a modulation scheme, a bandwidth, precodinginformation, a used channel, transmission power, and the like. By doingso, even if the aircraft 1 is provided with a radio altimeter 2 thatoperates differently depending on the altitude, the communicationapparatus 500 can use transmission parameters that do not interfere withthe radio altimeter 2.

FIG. 29 to FIG. 33 show examples of the waveform of the signal from theradio altimeter 2. FIG. 29 shows a relationship between the time and thetransmission frequency of the radio altimeter 2 when the altitude islow, and FIG. 30 shows a relationship between the time and thetransmission frequency of the radio altimeter 2 when the altitude ishigh. When the navigation altitude of the aircraft 1 increases, theradio altimeter 2 changes its operation so as to lower the frequency ofthe triangle wave to be transmitted, as shown in FIG. 30. The altitudeinformation acquisition unit 507 of the communication apparatus 500acquires the altitude at which the radio altimeter 2 switches itsoperation and an operation pattern after the switching. This can becarried out by the communication apparatus 500 storing in advanceinformation on the frequency at which the radio altimeter 2 changes itsoperation, receiving and observing a transmission signal from the radioaltimeter 2, or receiving notification from another communicationapparatus that holds information on the frequency of the radio altimeter2. The altitude information acquisition unit 507 notifies thecommunication controller 504 of the current altitude, the altitude atwhich the radio altimeter 2 switches its operation, and the operationpattern. The communication controller 504 determines the transmissionparameters of the communication apparatus 500 based on the informationreceived from the altitude information acquisition unit 507. Thecommunication controller 504 transmits transmission data to the encoder505. The encoder 505 performs encoding processing on the transmissiondata according to the parameters determined by the communicationcontroller 504, and generates encoded data. The transmitter 506modulates the encoded data and transmits it from the antenna 511.

This embodiment described an example of the radio altimeter 2 thatchanges the value of the frequency of the triangular wave according tothe altitude, but the present disclosure is not limited to this. Forexample, the radio altimeter 2 may change the bandwidth swept at thefrequency shown in FIG. 31 to the bandwidth shown in FIG. 32, or theradio altimeter 2 may change the number of triangle waves to betransmitted as shown in FIG. 33. Even with these radio altimeters 2, thecommunication controller 504 can transmit a transmission signal withappropriate transmission parameters in accordance with the change in theoperation of the radio altimeter.

Embodiment 6

The present embodiment describes a communication apparatus that performscontrol of communication conditions such as transmission power inaccordance with the location at which the communication apparatus isinstalled.

FIG. 34 shows an example of the positional relation between a pluralityof communication apparatuses 600 (600 a to 600 c) in the aircraft 1. Thecontrol apparatus 6100 is a wireless base station, and performscommunication with the communication apparatus 600 a, the communicationapparatus 600 b, and the communication apparatus 600 c. The controlapparatus 6100 controls the communication conditions of communicationwith each of the communication apparatuses 600 a to 600 c.

FIG. 35 shows a configuration of the control apparatus 6100. The controlapparatus 6100 comprises an antenna 6111, a receiver 6102, a decoder6103, a communication controller 6104, a position informationacquisition unit 6107, an encoder 6105, and a transmitter 6106. Theposition information acquisition unit 6107 acquires position informationof the radio altimeter 2 and position information where the plurality ofcommunication apparatuses 600 a to 600 c with which the controlapparatus 6100 communicate are installed, and stores the positioninformation in a memory. The position information acquisition unit 6107can adopt, as means for acquiring the position information of eachcommunication apparatus 600 a to 600 c, a method of estimating theposition from the reception power and transmission path response duringcommunication with each communication apparatus 600 a to 600 c, or amethod of saving a table in which the position of each communicationapparatus 600 a to 600 c is recorded and referring to the table.

FIG. 36 shows the configuration of the communication apparatus 600 (600a to 600 c). The communication apparatus 600 comprises an antenna 611, areceiver 602, a decoder 603, a communication controller 604, a controlinformation storage 607, an encoder 605, a transmitter 606, and atransmission power controller 608.

The control information storage 607 is, for example, a memory, andstores control information for communication that is notified from thecontrol apparatus 6100. The communication controller 604 acquires, fromthe control information storage 607, control information required fortransmission and reception of a radio signal.

The communication apparatus 600 includes a processor 610 includingelectronic circuitry such as a CPU. The processor 610 executes thefunctions of the decoder 603, the communication controller 604, theencoder 605, and the transmission power controller 608 by performingcontrol and calculation according to a predetermined algorithm.

The communication procedure of the control apparatus 6100 and thecommunication apparatus 600 will be described. In this example, theradio altimeter 2 is installed at an external front bottom portion ofthe fuselage of aircraft. The position information acquisition unit 6107of the control apparatus 6100 is assumed to acquire the positioninformation of the communication apparatus 600 a, the communicationapparatus 600 b, and the communication apparatus 600 c. The radioaltimeter 2 is installed at the front bottom portion of the fuselage ofaircraft, and therefore, the effect of interference with the radioaltimeter is great at the communication apparatus 600 a installed at awindow side in the front of the fuselage, and smaller at thecommunication apparatus 600 b installed in a central portion of thefuselage and at the communication apparatus 600 c installed at a windowside in the rear of the fuselage. When the control apparatus 6100performs communication with the communication apparatus 600 a, theposition information acquisition unit 6107 of the control apparatus 6100acquires the position information of the communication apparatus 600 aand transmits the position information to the communication controller6104. The communication controller 6104 determines, on the basis of theposition information of the communication apparatus 600 a, acommunication condition to be used by the communication apparatus 600 afor communication. In this example, since the communication apparatus600 a is positioned at a window side in the front of the fuselage wherethere is risk of causing interference with the radio altimeter 2, thecommunication controller sets a condition of using a low transmissionpower, and creates transmission data for notifying the communicationapparatus 600 a of that condition. The communication controller 6104transmits the transmission data to the encoder 6105. The encoder 6105encodes the transmission data, and transmits the encoded data to thetransmitter 6106. The transmitter 6106, after modulating the encodeddata into a form that can be transmitted by a radio signal, transmitsthe signal from the antenna 6111.

The communication apparatus 600 a receives the signal from the controlapparatus 6100 via the antenna 611. The receiver 602 demodulates thereceived signal and creates demodulation data. The decoder 603 decodesdigitalized demodulation data to obtain reception data. Thecommunication controller 604 decodes the reception data, obtains thecommunication condition notified from the control apparatus 6100, andstores the communication condition in the control information storage607. In this case, the condition of low transmission power is saved.When the communication apparatus 600 a transmits a signal to the controlapparatus 6100 or another communication apparatus, the communicationcontroller 604 reads the communication condition stored in the controlinformation storage 607 and determines transmission parameters thatconform to that condition. The communication controller 604 transmitstransmission data to the encoder 605. The encoder 605 creates encodeddata in accordance with the determined transmission parameters. Thetransmitter 606 modulates the encoded data in accordance with thedetermined transmission parameters, and converts it into a formtransmittable as a radio signal. At this time, the transmission powercontroller 608 controls the transmission power of the radio signal inaccordance with the transmission parameters determined by thecommunication controller 604. In this case, the transmission powercontroller 608 makes the transmission power lower than a predeterminedvalue.

On the other hand, when performing communication with the communicationapparatus 600 b, the communication controller 6104 of the controlapparatus 6100 determines the effect of interference with the radioaltimeter 2 by the communication apparatus 600 b to be small on thebasis of the position information of the communication apparatus 600 b.Based on this determination, the communication controller 6104 sets acondition of using a high transmission power as the communicationcondition to be used by the communication apparatus 600 b forcommunication, and creates transmission data for notifying thecommunication apparatus 600 b of that condition. The communicationapparatus 600 b, having received the transmission data from the controlapparatus 6100, stores the communication condition received from thecontrol apparatus 6100 in the control information storage 607. In thiscase, the control information storage 607 saves the condition of hightransmission power. When the communication apparatus 600 b transmits asignal to the control apparatus 6100 or another communication apparatus,the communication controller 6104 reads the communication conditionstored in the control information storage 607 and determinestransmission parameters that conform to that condition. Thecommunication controller 604 transmits the transmission data to theencoder 605. The encoder 605 creates encoded data in accordance with thedetermined transmission parameters. The transmitter 606 modulates theencoded data in accordance with the determined transmission parameters,and converts it into a form transmittable as a radio signal. At thistime, the transmission power controller 608 controls the transmissionpower of the radio signal in accordance with the transmission parametersdetermined by the communication controller 604. In this case, thetransmission power controller 608 makes the transmission power higherthan a predetermined value.

Control in the case of the control apparatus 6100 communicating with thecommunication apparatus 600 c is the same as the case of the controlapparatus 6100 communicating with the communication apparatus 600 b.

With the above described communication control, the control apparatus6100 can set a low transmission power for the communication apparatus600 with a high possibility of causing interference with the radioaltimeter 2 and a high transmission power for the communicationapparatus 600 with a low possibility of causing interference with theradio altimeter 2, according to the position information of thecommunication apparatuses 600. Accordingly, it is possible to constructa WAIC network capable of coexisting with the radio altimeter 2.

In the embodiments that have been described above and the embodimentsthat will be discussed below, a control apparatus including the controlapparatus 6100 is provided independently of a communication apparatus.Alternatively, one of a plurality of communication apparatuses mayinclude a function of the control apparatus, which is for example afunction of the communication controller 604 of the communicationapparatus 600. In this case, each communication apparatus 600 may havethe function of managing the position information.

In a case where the communication apparatus 600 is attached to a mobilebody so as to be movable, the control apparatus 6100 may estimate adistance between the communication apparatus 600 and the radio altimeter2, and based on the estimation, update the position information of thecommunication apparatus 600.

In the present embodiment, description was made using the positionalrelation of the control apparatus 6100, the communication apparatuses600 and the radio altimeter 2 shown in FIG. 34, but the presentembodiment is not limited thereto. The similar effect as the aboveexample can be obtained with a different number of communicationapparatuses 600 or with different positions of the control apparatus6100, the communication apparatus 600 and the radio altimeter 2. As anexample, when the radio altimeter 2 is installed at a rear bottomportion of the fuselage of aircraft, the control apparatus 6100 performscontrol that lowers transmission power of the communication apparatus600 c. When the communication apparatus 600 is installed in a cargo areaat a lower layer of the fuselage, or installed outside the fuselage,such as on a wing or under the fuselage, the communication controller6104 of the control apparatus 6100, if determining that there is apossibility of the communication apparatus 600 causing interference withthe radio altimeter 2 from the position information of suchcommunication apparatus 600, determines the communication condition tobe low transmission power and notifies the communication apparatus 600of the communication condition.

Embodiment 7

The control apparatus 6100 shown in FIG. 35 may perform control thatswitches a directivity pattern of the antenna 611 of the communicationapparatus 600 based on position information of the communicationapparatus 600. A communication procedure between the control apparatus6100 and the communication apparatus 600 in that case will be discussed.Here, the case of a radio altimeter 2 being installed at a front bottomportion of the fuselage of aircraft as shown in FIG. 34 will bediscussed. The antenna 611 of the communication apparatus 600 as shownin FIG. 36 is provided with a plurality of directivity patterns, withthe communication controller 604 switching between the directivitypatterns. The position information acquisition unit 6107 of the controlapparatus 6100 acquires the position information of the communicationapparatus 600 a, the communication apparatus 600 b, and thecommunication apparatus 600 c. When the radio altimeter 2 is installedat an external front bottom portion of the fuselage of aircraft, theeffect of interference with the radio altimeter 2 is great at thecommunication apparatus 600 a installed at a window side in the front ofthe fuselage, and small at the communication apparatus 600 b installedat a central portion of the fuselage and at the communication apparatus600 c installed at a window side in the rear of the fuselage. When thecontrol apparatus 6100 performs communication with the communicationapparatus 600 a, the position information acquisition unit 6107 of thecontrol apparatus 6100 transmits the position information of thecommunication apparatus 600 a to the communication controller 6104. Thecommunication controller 6104 determines a communication condition to beused by the communication apparatus 600 a for communication, on thebasis of the position information of the communication apparatus 600 a.Here, since the communication apparatus 600 a is positioned at thewindow side in the front of the fuselage where there is risk of causinginterference with the radio altimeter 2, the communication controller6104 sets the condition of selecting a directivity pattern in which itsmaximum gain is not oriented in the direction of the window, and createstransmission data for notifying the communication apparatus 600 a ofthat condition. The communication controller 6104 transmits thetransmission data to the encoder 6105. The encoder 6105 encodes thetransmission data, and transmits the encoded data to the transmitter6106. The transmitter 6106, after modulating the encoded data into aform that can be transmitted by a radio signal, transmits the signalfrom the antenna 6101 to the communication apparatus 600 a.

Accordingly, as shown in FIG. 37, the communication apparatus 600 a thatis installed at the window side in the front of the fuselage cantransmit the transmission signal using a beam pattern Dr-a whose maximumgain is at the front center side of the fuselage, and thereby can reduceinterference with the radio altimeter 2 installed at the front bottomportion of the fuselage.

For the control apparatus 6100 and the communication apparatuses 600 b,600 c that are installed at a position where interference with the radiodiameter 2 is relatively small, the beam patterns Dr-1, Dr-b, Dr-chaving normal maximum gains as shown in FIG. 37 are used.

Embodiment 8

The present embodiment describes a communication apparatus that isinstalled near a radio altimeter 2 and notifies other communicationapparatuses of the operation information of the radio altimeter 2. FIG.38 shows a radio altimeter 2 and a plurality of communicationapparatuses 800 (800 a to 800 c) that are installed in an aircraft 6.The communication apparatus 800 c is installed near the radio altimeter2 and can receive a signal transmitted by the transmitter 3 (FIG. 1) ofthe radio altimeter 2.

FIG. 39 shows the configuration of a communication apparatus 800. Thecommunication apparatus 800 comprises an antenna 811, a receiver 802, adecoder 803, a communication controller 804, an altimeter informationmanagement unit 807, an altimeter information estimation unit 809, anencoder 805, and a transmitter 806.

The communication apparatus 800 includes a processor 810 includingelectronic circuitry such as a CPU. The processor 810 executes thefunctions of the decoder 803, the communication controller 804, theencoder 805, the altimeter information management unit 807, and thealtimeter information estimation unit 809 by performing control andcalculation according to a predetermined algorithm.

The altimeter information estimation unit 809 estimates information ofthe radio altimeter 2 from the signal of the radio altimeter 2 receivedby the receiver 802, specifically, from the frequency bandwidth beingused, the triangle wave frequency (frequency sweep rate), the timing ofthe frequency sweep, or the like. The altimeter information estimationunit 809 transmits estimated information on the radio altimeter 2 to thealtimeter information management unit 807. The altimeter informationmanagement unit 807 acquires the information on the radio altimeter 2and stores it in a memory, and transmits the information on the radioaltimeter 2 to the communication controller 804. Upon receiving anupdate value of the altitude information from the altimeter informationestimation unit 809, the altimeter information management unit 807updates the information stored in the memory. The communicationapparatus 800 (e.g. 800 c) notifies another one or other plurality ofthe communication apparatuses 800 (e.g. 800 a, 800 b) of the informationon the radio altimeter 2. The communication controller 804 createstransmission data including the information on the radio altimeter 2received from the altimeter information management unit 807. The encoder805 encodes the transmission data. The transmitter 806 modulates theencoded data, generates a transmission signal, and transmits the signalfrom the antenna 811.

As in the example shown in FIG. 38, even if the communicationapparatuses 800 a, 800 b cannot directly receive a signal from the radioaltimeter 2, the communication apparatuses 800 a, 800 b can obtainoperation information of the radio altimeter 2 that is estimated by thecommunication apparatus 800 c, which is capable of directly receivingthe signal from the radio altimeter 2. Accordingly, the communicationapparatuses 800 a, 800 b are capable of transmitting signals using acommunication system that does not cause interference with the radioaltimeter 2.

As shown in FIG. 39, the communication apparatus 800 c also comprises areceiver 802 and a decoder 803 and is capable of receiving not only asignal from the radio altimeter 2 but also signals from othercommunication apparatuses. The communication apparatus 800 c calculatesan SIR (signal-to-interference power ratio) from the power of thereceived signal from the radio altimeter 2 and from the power of thesignal received from another communication apparatus. When the SIR islow, that is, when the signal power received from the othercommunication apparatus is higher, the communication apparatus 800 ctransmits to the other communication apparatus a signal instructing achange in the communication condition. For example, the communicationapparatus 800 c gives an instruction of a change in the communicationcondition such as lowering transmission power, changing a beam pattern,changing the frequency bandwidth used, shifting the timing oftransmission, or the like.

When there are two or more other communication apparatuses 800 in theaircraft 16, the communication apparatus 800 c may periodicallybroadcast the information on the radio altimeter 2. This enables the twoor more other communication apparatuses 800 to be notified of theinformation on the radio altimeter 2. As a result, it is not necessaryto notify the two or more other communication apparatuses 800individually, and therefore, communication resources can be saved.

Embodiment 9

This embodiment describes a communication apparatus that transmitsnotice of a transmission timing that causes interference with the radioaltimeter 2 to other communication apparatuses using the same frequencychannel.

FIG. 40 shows the configuration of a communication apparatus 900according to this embodiment. The communication apparatus 900 has thesame configuration as the communication apparatus 200 (FIG. 9) accordingto Embodiment 2, and comprises an antenna 911, a receiver 902, a decoder903, a communication controller 904, an encoder 905, and a transmitter906. The communication apparatus 900 includes a processor 910 includingelectronic circuitry such as a CPU. The processor 910 executes thefunctions of the decoder 903, the communication controller 904, and theencoder 905 by performing control and calculation according to apredetermined algorithm.

The communication controller 904 of the communication apparatus 900acquires a transmission timing of the radio altimeter 2. Thecommunication controller 904 creates a transmission frame including atransmission prohibition time before the time when interference is givento the radio altimeter 2, and transmits the transmission frame to theencoder 905. The encoder 905 encodes the data of the transmission frameand transmits it to the transmitter 906. The transmitter 906 modulatesthe encoded data into a transmission signal, and transmits it to anothercommunication apparatus through the antenna 911.

The communication controller of another communication apparatus, whichhas the same configuration as that of the communication apparatus 900,receives and decodes the thus created transmission frame with thetransmission prohibition period, thereby acquiring the transmissionprohibition period.

The communication apparatus 900 may use an RTS frame of the IEEE 802.11standard as an example of a transmission frame including a transmissionprohibition period.

FIG. 41 shows a RTS system according to the IEEE 802.11 standard. Thecommunication controller of the communication apparatus 900 a creates anRTS frame in which the NAV is set for a longer period than the periodduring which the radio altimeter 2 is given interference. Thedestination address of the communication apparatus 900 b is described asa destination of the RTS frame. When the communication controller of thecommunication apparatus 900 b receives an RTS frame, it similarlycreates a CTS frame in which NAV is set and transmits it to anothercommunication apparatus.

Accordingly, the communication apparatus 900 a, another communicationapparatus 900 b that has received a RTS frame, still anothercommunication apparatus that has received a CTS frame, and still anothercommunication apparatus that has received both the RTS frame and the CTSframe are prevented from transmitting signals in the NAV period.Therefore, interference with the radio altimeter 2 does not occur. Theother communication apparatus can start carrier sense when apredetermined time elapses after NAV ends, and can perform transmissionwhen there is a transmission frame.

In the above description, the communication controller of thecommunication apparatus 900 a uses the address of the communicationapparatus 900 b as a destination of the RTS frame. However, the presentdisclosure is not limited to this. For example, a dummy address may bedescribed. Even in this case, although the communication apparatus thattransmits a CTS frame is absent, any other communication apparatus thatcan receive a signal from the communication apparatus 900 a can receivea RTS frame and read the NAV described therein, thereby setting atransmission prohibition period.

Even if the communication controller of the other communicationapparatus can not perform carrier sense on the transmission signal ofthe radio altimeter 2, it can estimate a transmission timing of theradio altimeter from accumulated NAV information described in RTSframes.

Embodiment 10

The present embodiment describes a communication apparatus that reducesinterference with the radio altimeter when relaying communicationbetween a control apparatus and a communication apparatus through aplurality of other communication apparatuses.

FIG. 42 shows a radio altimeter 2, a control apparatus 1000, andcommunication apparatuses 1001 a, 1001 b that are installed in theaircraft 1. Here, the radio altimeter 2 is installed at an externalfront bottom portion of the fuselage of aircraft 1. The case ofcommunication between the control apparatus 1000 and the communicationapparatus 1001 a will be considered.

FIG. 43 shows the configuration of a control apparatus 1000. The controlapparatus 1000 comprises an antenna 1011, a receiver 1002, a decoder1003, a communication controller 1004, a routing unit 1008, an encoder1005, and a transmitter 1006. The routing unit 1008 creates acommunication route between the control apparatus 1000 and thecommunication apparatus 1001 a. The communication route is created fromthe position of the radio altimeter 2, the positions of the plurality ofother communication apparatuses 1001, the position of the communicationapparatus 1001 a, and the position of the control apparatus 1000. As aguideline of route creation by the routing unit 1008, a communicationapparatus that has a high possibility of causing interference with theradio altimeter 2 is not included in the communication route. In otherwords, the routing unit 1008 creates a communication route using thecommunication apparatuses in the central portion of the fuselage, asshown in FIG. 42, without using, for example, the communicationapparatus 1001 b that is installed at a window side at the front of thefuselage. When the control apparatus 1000 transmits a signal to thecommunication apparatus 1001 a, the communication controller 1004creates transmission data, including communication path information tothe communication apparatus 1001 a, with the data being addressed to thecommunication apparatus serving as a next relay node. The encoder 1005encodes the transmission data. The transmitter 1006 modulates theencoded data, and after converting the modulated data into a formtransmittable by radio signal, transmits the signal from the antenna1011. The communication apparatus 1001 c that has received thetransmission signal from the control apparatus 1000 obtains an addressof the communication apparatus 1001 d serving as a next relay node basedon the transmission path information included in the reception data, andtransmits the relay data to that address.

The control apparatus 1000 of the present embodiment creates acommunication route that does not include a communication apparatus 1001b installed at a window side of the front of the fuselage. As a result,the control apparatus 1000 can perform communication with thecommunication apparatus 1001 a without using the communication apparatus1001 b that has a possibility of causing interference with the radioaltimeter 2.

In the present embodiment, attention was focused only on the case ofcommunication between the control apparatus 1000 and the communicationapparatus 1001 a. However, in the actual environment, the controlapparatus 1000 performs communication with the plurality ofcommunication apparatuses simultaneously. Communication among thecommunication apparatuses may also occur. In such a case, when using acommunication route that excludes communication apparatuses that have apossibility of causing interference with the radio altimeter 2, there isrisk of communication traffic being concentrated at a specific relaynode. Concentration of communication traffic at a specific relay nodeleads to a drop in throughput.

For such a phenomenon, it is possible to avoid a drop in throughput byperforming control of raising transmission power of a communicationapparatus with a low possibility of causing interference with the radioaltimeter 2, as performed by the control apparatus 6100 in Embodiment 6.Particularly, the control apparatus 1000 may increase communicationcapacity between the relay nodes by increasing transmission power of thecommunication apparatuses included in the communication route and at thesame time raising their MCS, thereby improving the throughput.

The control apparatus 1000 may create a communication route that doesnot use the communication apparatus 1001 c installed at a widow side ofthe rear of the fuselage of the aircraft 1, which has a possibility ofcausing interference with the radio altimeter 2 of another aircraft.This can reduce the effect of interference with the radio altimeter 2 ofthe other aircraft. In addition, in order for the control apparatus 1000to acquire the position of the aircraft 9, the information may beacquired by connecting to a radar installed on the aircraft 1 orconnecting to a device that collects information necessary fornavigation.

Embodiment 11

This embodiment describes a communication apparatus that reducesinterference with a radio altimeter of nearby aircraft.

FIG. 44 illustrates positions of aircraft 1 a-to 1 d present on anairport runway and taxiway. In this embodiment, a configuration and anoperation of the communication apparatus will be discussed by taking acase where the aircraft 1 b, the aircraft 1 c, and the aircraft 1 d areon the taxiway, and the aircraft 1 a in the sky is about to land on therunway. If the communication apparatuses of the aircraft 1 b to 1 dperform WAIC communication using the 4.2 GHz to 4.4 GHz band, this wouldinterfere with the radio altimeter of the landing aircraft 1 a. Thecommunication apparatus in this embodiment is a communication apparatusthat performs WAIC communication in consideration of the frequency andtime used by the radio altimeter of the aircraft 1 a and the positionalrelationship with the aircraft 1 a.

FIG. 45 shows the configuration of a communication apparatus 1100installed in the aircraft 1 b. The communication apparatus 1100comprises an antenna 1111, a receiver 1102, a decoder 1103, acommunication controller 1104, an encoder 1105, a transmitter 1106, aresource information acquisition unit 1107, and a transmission powercontroller 1108.

The communication apparatus 1100 comprises a processor 1110 includingelectronic circuitry such as a CPU. The processor 1110 executes thefunctions of the decoder 1103, the communication controller 1104, theencoder 1105, the resource information acquisition unit 1107, and thetransmission power controller 1108 by performing control and calculationaccording to a predetermined algorithm.

The communication apparatus 1100 transmits a signal received by theantenna 1111 to the receiver 1102. The receiver 1102 performs receptionprocessing and transmits the received signal, which has been digitized,to the decoder 1103. The decoder 1103 decodes the received signal toextract reception data. The communication controller 1104 reads adestination address included in the reception data, and when thereception data is addressed to the communication apparatus itself,performs processing of the reception data.

The resource information acquisition unit 1107 acquires transmissionfrequencies and timings of a plurality of adjacent radio altimeters 2and/or directions in which adjacent aircraft exist (hereinafter referredto as resource information). The communication controller 1104 controlsparameters or communication conditions such as transmission power, adirectivity, a using frequency band, and a transmission timing, based onthe acquired resource information.

When the communication apparatus 1100 transmits a signal to anothercommunication apparatus, the communication controller 1104 acquiresresource information from the resource information acquisition unit1107. The communication controller 1104 generates data to be transmittedand determines transmission parameters based on the acquired resourceinformation. The transmission parameters may include an antennadirectivity, a coding scheme, a coding rate, a modulation scheme, abandwidth, precoding information, a using channel, a transmissiontiming, transmission power, and the like. The communication controller1104 transmits transmission data to the encoder 1105. The encoder 1105performs an encoding process on the transmission data according to theparameters determined by the communication controller 1104 to generateencoded data. The transmitter 1106 modulates the encoded data accordingto the parameters determined by the communication controller 1104, andtransmits the modulated data from the antenna 1101. At this time, thetransmission power controller 1108 performs control so that thetransmission power of the transmission signal transmitted from thetransmitter 1106 has a value of the transmission power determined by thecommunication controller 1104.

(1) Resource Control Using a Position of the Aircraft 1 a

The resource information acquisition unit 1107 acquires positioninformation of the aircraft 1 a. The resource information acquisitionunit 1107 can use, as means for acquiring position information of theaircraft 1 a, control information from the airport control tower,information from radar mounted on the aircraft 1 a, or the like. Theresource information acquisition unit 1107 acquires a positionalrelationship between the aircraft 1 b and the aircraft 1 a from theposition information of the aircraft 1 a acquired by the above means.When the communication controller 1104 transmits a signal to anotherWAIC communication apparatus, the communication controller 1104 acquiresinformation on the positional relationship between the aircraft 1 b andthe aircraft 1 a from the resource information acquisition unit 1107,and based on the information, determines a directivity pattern of theantenna 1101 for transmitting a transmission signal. The criterion fordetermining the directivity pattern may adopt, for example, using apattern with a reduced gain in a direction in which the aircraft 1 aexists.

In this way, the communication apparatus 1100 can reduce the amount ofradio waves emitted in the direction in which the aircraft 1 a exists.Therefore, interference with the radio altimeter of the aircraft 1 aduring its landing can be reduced.

(2) Resource Control Using Information on a Transmission Frequency ofthe Radio Altimeter of the Aircraft 1 a

The resource information acquisition unit 1107 acquires a frequency ofthe signal transmitted by the radio altimeter of the aircraft 1 a. Whentransmitting a signal to another WAIC communication apparatus, thecommunication controller 1104 acquires, from the resource informationacquisition unit 1107, information on the frequency used by the radioaltimeter of the aircraft 1 a, and based on the information, determinesa frequency channel or transmission timing for signal transmission. Forexample, as shown in FIG. 2, the transmission frequency of the radioaltimeter 2 changes with time within a predetermined frequency range,and therefore, by using a frequency channel including a frequency thatthe radio altimeter 2 does not use, it is possible to avoid interferencewith the radio altimeter. In a case where the communication apparatus1100 can transmit a signal only on a predetermined frequency channel, itis possible to avoid interference with the radio altimeter 2 byacquiring the time when the radio altimeter 2 does not use a frequencyof the corresponding frequency channel and transmitting a WAICcommunication signal in that time.

In this embodiment, a configuration and an operation of thecommunication apparatus 1100 of the aircraft 1 b have been describedwith respect to the radio altimeter of the aircraft 1 a of FIG. 44, butthe present disclosure is not limited to this. Interference with a radioaltimeter can be reduced and avoided by the same configuration andoperation in the aircraft 1 c or the aircraft 1 d.

The communication apparatus 1100 may transmit transmission dataaccording to a communication condition including only transmissionfrequency and/or transmission timing of the transmission data, withoutperforming control of the transmission power.

The communication apparatus 1100 may transmit the acquired resourceinformation and the determined communication condition to anothercommunication apparatus so that the other communication apparatus canuse those information. In this case, the communication apparatus 1100may be a control apparatus that manages all other communicationapparatuses, similarly to the control apparatus 6100 of Embodiment 6.

Embodiment 12

As shown in FIG. 46, when there is another aircraft in the vicinity ofthe aircraft 1, the communication apparatus in the aircraft 1 mayinterfere with the radio altimeter installed in the other aircraft. Acase where an aircraft 9 is present behind a port side of the aircraft 1as shown in FIG. 46 will be discussed.

The control apparatus 1200 has the same configuration as thecommunication apparatus of the other embodiments, such as the controlapparatus 6100 of Embodiment 6. Each of the communication apparatuses1201 a to 1201 c has the same configuration as the communicationapparatus of the other embodiments, such as the communication apparatus200 of Embodiment 2, the communication apparatus 600 of Embodiment 6, orthe communication apparatus 1100 of Embodiment 11.

In this case, a transmission signal from the communication apparatus1201 c of the aircraft 1 causes interference with the radio altimeter 2installed at an external bottom front of the fuselage of the aircraft 9.The communication controller of the control apparatus 1200 createstransmission data including a transmission condition for reducing thetransmission power of the communication apparatus 1201 c, and transmitsthe transmission data to the communication apparatus 1201 c.

By doing so, the communication apparatus 1201 c can performcommunication while reducing an influence of interference to the radioaltimeter 2 of the aircraft 9. In order for the position informationacquisition unit of the control apparatus 1200 to acquire a position ofthe aircraft 9, an approach to acquire the information may be taken byconnecting to radar installed in the aircraft 1 or connecting to adevice that collects information necessary for navigation.

Embodiment 13

FIG. 47 shows a positional relationship between the radio altimeter 2,the communication apparatus 1300 a, and the communication apparatus 1300b installed in the aircraft 1. In this embodiment, the communicationapparatus 1300 a and the communication apparatus 1300 b that cantransmit and receive a radio signal even when there is interference withthe radio altimeter 2 will be discussed.

In FIG. 47, the following case will be discussed. A transmission signalof the radio altimeter 2 does not reach the communication apparatus 1300a, and therefore, is received with low power that can be regarded asnoise. On the other hand, in the communication apparatus 1300 b, atransmission signal of the radio altimeter 2 is received as aninterference signal. The transmission signal of the communicationapparatus 1300 a does not reach the radio altimeter 2, but reaches thecommunication apparatus 1300 b. In other words, the communicationapparatus 1300 a and the radio altimeter 2 do not interfere with eachother, but the communication apparatus 1300 b can receive a radio signalfrom both the communication apparatus 1300 a and the radio altimeter 2.

FIG. 48 and FIG. 49 illustrate spectra 131 a and 131 b that can beobserved at a reception end of the communication apparatus 1300 b. InFIG. 48, the spectrum 131 b, which is a spectrum of a received signalfrom the communication apparatus 1300 a, and the spectrum 131 a, whichis a spectrum of an interference signal from the radio altimeter 2, havedifferent frequencies. Therefore, in this case, the communicationapparatus 1300 b can receive a transmission signal from thecommunication apparatus 1300 a without interference. However, as shownin FIG. 49, when the frequencies of the spectrum 131 a and the spectrum131 b are the same or overlapped, a signal from the radio altimeter 2becomes interference, and the quality of a signal from the communicationapparatus 1300 a received by the communication apparatus 1300 bdeteriorates. In order to avoid this, the transmitter of each of thecommunication apparatuses 1300 a and 1300 b of this embodiment has aconfiguration shown in FIG. 50. The transmitter 1310 includes an encoder1311, an interleaving unit 1312, a modulator 1313, a multicarriermodulator 1314, an output unit 1315, and an antenna 1316.

The encoder 1311 performs error correction encoding on transmissiondata. Here, the encoder 1311 uses an encoding scheme having a codelength that is the same as or longer than the number of bits included inone symbol of a multicarrier modulation signal generated by themulticarrier modulator 1314. The interleaving unit 1312 rearranges theorder of encoded transmission data. Specifically, the interleaving unit1312 rearranges the order of transmission data with a size that is thesame as or longer than the code length of the encoding scheme used bythe encoder 1311. The modulator 1313 creates a modulated signal such asQPSK or QAM using the interleaved transmission data. The multicarriermodulator 1314 generates a single multicarrier modulation signal from aplurality of modulation signals. The output unit 1315 performs waveformshaping filter processing and frequency conversion processing on themulticarrier modulation signal, generates a radio signal waveform, andtransmits it from the antenna 1316.

Since the transmitter 1310 uses a multicarrier modulation signal as aradio signal, even when the spectrum 131 a of the radio altimeter 2 usesthe same frequency as the spectrum 131 b of the transmission signal ofthe communication apparatus 1300 a as shown in FIG. 51 to FIG. 54, onlysome subcarriers of the multicarrier modulation signal are affected bythe interference whereas the other subcarriers are not affected by theinterference as shown in FIG. 52, FIG. 53, and FIG. 54. In addition, theencoder 1311 of the transmitter 1310 performs encoding processing with acode length that is the same as or longer than the number of bits of onesymbol of the multicarrier modulation signal, and the interleaving unit1312 rearranges the encoded bit sequence with a size that is the same asor longer than the code length. Accordingly, even if some subcarriers ofthe multicarrier modulation signal are affected by the interference andthe reception quality deteriorates, reception errors due to theinfluence of interference can be corrected in a decoding process of thecommunication apparatus 1300 b on a receiving side.

By using the communication apparatus 1300 a of the present embodiment,it is possible to transmit a radio signal to the communication apparatus1300 b with high reception quality even in an environment whereinterference with the radio altimeter 2 exists.

In addition, in this embodiment, the case where the radio altimeter 2interferes with the communication apparatus 1300 b has been described.The same effect can be obtained even when, for example, a plurality ofaircraft are present nearby as shown in FIG. 44 and the radio altimeter2 installed in the other aircraft is an interference source.

REFERENCE NUMERALS

1 . . . Aircraft, 2 . . . Radio altimeter, 3 . . . Transmitter, 4 . . .Receiver, 9 . . . Aircraft, 10 b . . . Bottom part, 16 . . . Aircraft,22 . . . Frequency mixer, 24 . . . Reception LPF, 26 . . . Frequencycounter, 27 . . . Altitude alarm, 28 . . . Altitude indicator, 29 . . .Sweep generator, 30 . . . voltage control oscillator, 31 . . . Bufferamplifier, 100, 200, 300, 300 a to 300 b, 400, 500, 600, 600 a to 600 c,800, 800 a to 800 c, 900, 900 a to 900 b, 1000, 1000 a to 1000 d, 1100,1200, 1201 a to 1201 c, 1300 a to 1300 b . . . Communication apparatus,102, 202, 302, 402, 502, 602, 802, 902, 1002, 1102, 6102 . . . Receiver,103, 203, 303, 403, 503, 603 803, 903, 1003, 1103, 6103 . . . Decoder,104, 204, 304, 404, 504, 604, 804, 904, 1004, 1104, 6104 . . .Communication controller, 105, 205, 305, 405, 505, 605 805, 905, 1005,1105, 6105 . . . Encoder, 106, 206, 306, 406, 506, 606, 806, 906, 1006,1106, 6106 . . . Transmitter, 107, 507 . . . Altitude informationacquisition unit, 108, 608, 1108 . . . Transmission power controller,110, 210, 310, 410, 510, 610, 810, 910, 1110 . . . Processor, 111, 211,311, 511, 611, 811, 911, 1011, 1101, 1111 6101, 6111 . . . Antenna, 131a . . . Spectrum, 131 b . . . Spectrum, 411 . . . Antenna array, 312 . .. Interleaving unit, 607 . . . Control information storage, 807 . . .Altimeter information management unit, 809 . . . Altimeter informationestimation unit, 1000, 6100 . . . Controller, 1008 . . . Routing unit,1107 . . . Resource information acquisition unit, 1310 . . .Transmitter, 1311 . . . Encoder, 1312 . . . Interleaving unit, 1313 . .. Modulator, 1314 . . . Multicarrier modulator, 1315 . . . Output unit,1316 . . . Antenna, 6107 . . . Position information acquisition unit

PRIOR ART DOCUMENT Patent Document [Patent Document 1] US PatentApplication Publication No. 2017/0176588 [Patent Document 1] US PatentApplication Publication No. 2017/0180072 [Patent Document 1] US PatentApplication Publication No. 2017/0181146

1. A communication apparatus configured to be installed in an aircraftand communicate wirelessly with one other communication apparatus, thecommunication apparatus comprising: a controller configured to acquirealtitude information of the aircraft and determine transmission poweraccording to the altitude information; and a transmitter configured totransmit transmission data to the one other communication apparatususing the determined transmission power.
 2. The communication apparatusaccording to claim 1, wherein an operating frequency band of thecommunication apparatus includes a transmission frequency band of aradio altimeter installed in the aircraft.
 3. The communicationapparatus according to claim 1, wherein the controller is configured toincrease the transmission power when a value of the altitude informationis greater than a predetermined value and configured to decrease thetransmission power when the value of the altitude information is lessthan or equal to the predetermined value.
 4. The communication apparatusaccording to claim 3, wherein the controller is configured to increasethe transmission power as the value of the altitude information is lowerwhile the value of the altitude information is less than or equal to thepredetermined value.
 5. The communication apparatus according to claim1, wherein the controller is configured to change an encoding/modulationscheme for the transmission data according to the transmission power. 6.The communication apparatus according to claim 1, wherein the controlleris configured to: acquire position information of a radio altimeterinstalled in the aircraft and position information of the one othercommunication apparatus; and based on a position of the radio altimeterand a position of the one other communication apparatus, determine acommunication condition to be used in communication with the one othercommunication apparatus, and the transmitter is configured to transmitthe transmission data to the one other communication apparatus accordingto the communication condition.
 7. The communication apparatus accordingto claim 6, comprising an antenna, wherein the communication conditionincludes at least one of the transmission power and a directivitypattern of the antenna.
 8. The communication apparatus according toclaim 1, wherein the controller is configured to: detect a time when asignal is transmitted from a radio altimeter installed in the aircraft;and change a unit length of the transmission data so that the time isnot used for transmission of the transmission data.
 9. The communicationapparatus according to claim 1, wherein the controller is configured tocontrol a frequency spectrum of the transmission data so as not to use atransmission frequency of a signal from a radio altimeter installed inthe aircraft.
 10. The communication apparatus according to claim 9,wherein the controller is configured to control the frequency spectrumso that a component of the transmission data is not included in afrequency band lower than a cutoff frequency of an LPF applied to areceived signal of the radio altimeter.
 11. The communication apparatusaccording to claim 1, comprising a plurality of antennas whosedirectivities can be controlled, wherein the controller is configured tochange at least one of amplitude and a phase of a signal received byeach of the plurality of antennas, and controls so that the amplitude ofsynthesized signal is minimized.
 12. The communication apparatusaccording to claim 1, wherein the controller is configured to determinea communication condition for the transmission data and transmit thecommunication condition to a plurality of other communicationapparatuses.
 13. A communication control method for wirelesscommunication with one other communication apparatus in an aircraft, themethod including: acquiring altitude information of the aircraft;determining transmission power according to the altitude information;and transmitting transmission data to the one other communicationapparatus using the determined transmission power.